Pre-coating (EPCE®) UF membranes for direct treatment of surface water

The feasibility of ultra and microfiltration depends strongly on the achieved net flux. Direct treatment of surface water frequently results in low net fluxes and high cleaning frequencies. This is largely determined by the quality of the feed water and the mechanisms that determine the fouling and the fouling rate of the membranes. Controlling and preferably reducing the rate of fouling is a major challenge. Research has been carried out to reduce fouling to achieve a stable operation at an economical feasible net flux. This research investigates decreasing the membrane contact area for suspended and colloidal matter by a dynamic filter, i.e. Enhanced Pre-Coat Engineering (EPCE). The general applicability and the effects on the membrane performance of this new approach, has been determined on different water sources and with different pre-coat materials. Pre-coating results initially in a higher fouling rate, however this fouling rate stabilises after several filtration cycles. The stabilisation is caused by a better restoration of the permeability after a backwash and an enhanced backwash. From this research it can be concluded that EPCE is a promising technique to increase membrane performance. Long term effects, costs and full-scale implementation need to be demonstrated.

The preliminary results of this study show that: Pre-coating increases the fouling rate. This fouling rate stabilises after several filtration cycles. Pre-coating results in a better restoration of the permeability after a backwash or an enhanced backwash. The total amount of fouling stabilises after several filtration cycles. Nominal particle size and particle characteristics of the pre-coat material seem to influence the membrane performance. Bigger particles seem to restore the membrane better after a backwash or enhanced backwash. Smaller particles seem to give a lower rate of fouling. Effects of particle size and particle characteristics need to be determined. Comparison of direct treatment or in-line coagulation with pre-coating should be based on a number of filtration cycles, including several enhanced backwashes, that ensures that either both processes are stabilised or the permanent fouling of the unstable process exceeds that of the stable process. Of the tested pre-coat materials Diatomite, Powdered Activated Carbon, Kaolinite and iron oxide seem to have the best pre-coat characteristics. EPCE is a promising technique to increase membrane performance. Long-term effects, costs and full-scale implementation need to be demonstrated.